• Special Issue
  • Plasma/Laser Diagnostics
  • 11 Article (s)
Hard x-ray transmission curved crystal spectrometers (10–100 keV) for laser fusion experiments at the ShenGuang-III laser facility
Ming-hai Yu, Guang-yue Hu, Ning An, Feng Qian, Yu-chi Wu, Xiao-ding Zhang, Yu-qiu Gu, Qiu-ping Wang, and Jian Zheng
Two transmission curved crystal spectrometers are designed to measure the hard x-ray emission in the laser fusion experiment of Compton radiography of implosion target on ShenGuang-III laser facility in China. Cylindrically curved ${\it\alpha}$-quartz (10–11) crystals with curvature radii of 150 and 300 mm are used to cover spectral ranges of 10–56 and 17–100 keV, respectively. The distance between the crystal and the x-ray source can be changed over a broad distance from 200 to 1500 mm. The optical design, including the integral reflectivity of the curved crystal, the sensitivity, and the spectral resolution of the spectrometers, is discussed. We also provide mechanic design details and experimental results using a Mo anode x-ray source. High-quality spectra were obtained. We confirmed that the spectral resolution can be improved by increasing the working distance, which is the distance between the recording medium and the Rowland circle.
High Power Laser Science and Engineering
  • Publication Date: Feb. 09, 2016
  • Vol.4 Issue, 1 010000e2 (2016)
Hydrodynamic instability experiments with three-dimensional modulations at the National Ignition Facility
V.A. Smalyuk, S.V. Weber, D.T. Casey, D.S. Clark, J.E. Field, S.W. Haan, A.V. Hamza, D.E. Hoover, O.L. Landen, A. Nikroo, H.F. Robey, and C.R. Weber
The first hydrodynamic instability growth measurements with three-dimensional (3D) surface-roughness modulations were performed on CH shell spherical implosions at the National Ignition Facility (NIF) [G. H. Miller, E. I. Moses, and C. R. Wuest, Opt. Eng. 43, 2841 (2004)]. The initial capsule outer-surface amplitudes were increased approximately four times, compared with the standard specifications, to increase the signal-to-noise ratio, helping to qualify a technique for measuring small 3D modulations. The instability growth measurements were performed using x-ray through-foil radiography based on time-resolved pinhole imaging. Averaging over 15 similar images significantly increased the signal-to-noise ratio, making possible a comparison with 3D simulations. At a convergence ratio of , the measured modulation levels were times larger than those simulated based on the growth of the known imposed initial surface modulations. Several hypotheses are discussed, including increased instability growth due to modulations of the oxygen content in the bulk of the capsule. Future experiments will be focused on measurements with standard 3D ‘native-roughness’ capsules as well as with deliberately imposed oxygen modulations.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e17 (2015)
Measurements of the ablation-front trajectory and low-mode nonuniformity in direct-drive implosions using x-ray self-emission shadowgraphy
D.T. Michel, A.K. Davis, W. Armstrong, R. Bahr, R. Epstein, V.N. Goncharov, M. Hohenberger, I.V. Igumenshchev, R. Jungquist, D.D. Meyerhofer, P.B. Radha, T.C. Sangster, C. Sorce, and D.H. Froula
Self-emission x-ray shadowgraphy provides a method to measure the ablation-front trajectory and low-mode nonuniformity of a target imploded by directly illuminating a fusion capsule with laser beams. The technique uses time-resolved images of soft x-rays ( keV) emitted from the coronal plasma of the target imaged onto an x-ray framing camera to determine the position of the ablation front. Methods used to accurately measure the ablation-front radius (), image-to-image timing ( ps) and absolute timing ( ps) are presented. Angular averaging of the images provides an average radius measurement of and an error in velocity of . This technique was applied on the Omega Laser Facility [Boehly et al., Opt. Commun. 133, 495 (1997)] and the National Ignition Facility [Campbell and Hogan, Plasma Phys. Control. Fusion 41, B39 (1999)].
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e19 (2015)
An efficient method for unfolding kinetic pressure driven VISAR data
M. Hess, K. Peterson, and A. Harvey-Thompson
Velocity Interferometer System for Any Reflector (VISAR) [Barker and Hollenbach, J. Appl. Phys. 43, 4669 (1972)] is a well-known diagnostic that is employed on many shock physics and pulsed-power experiments. With the VISAR diagnostic, the velocity on the surface of any metal flyer can be found. For most experiments employing VISAR, either a kinetic pressure [Grady, Mech. Mater. 29, 181 (1998)] or a magnetic pressure [Lemke et al., Intl J. Impact Eng. 38, 480 (2011)] drives the motion of the flyer. Moreover, reliable prediction of the time-dependent pressure is often a critical component to understanding the physics of these experiments. Although VISAR can provide a precise measurement of a flyer’s surface velocity, the real challenge of this diagnostic implementation is using this velocity to unfold the time-dependent pressure. The purpose of this paper is to elucidate a new method for quickly and reliably unfolding VISAR data.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e22 (2015)
An important criterion for reliable multi-monochromatic x-ray imager diagnostics and its impact on the reconstructed images
T. Nagayama, R.C. Mancini, D. Mayes, R. Tommasini, and R. Florido
Temperature and density asymmetry diagnosis is critical to advance inertial confinement fusion (ICF) science. A multi-monochromatic x-ray imager, MMI, records the spectral signature from an ICF implosion core with time resolution, 2D spatial resolution and spectral resolution. While narrow-band images and 2D space-resolved spectra from the MMI data constrain the temperature and the density spatial structure of the core, the accuracy of the images and the spectra highly depends on the quality of the MMI data and the processing tools. Here, we synthetically investigate the criterion for reliable MMI diagnostics and its effects on the accuracy of the reconstructed images. The pinhole array tilt determines the object spatial sampling efficiency and the minimum reconstruction width, . When the spectral width associated with is significantly narrower than the spectral linewidth, the line images reconstructed from the MMI data become reliable. The MMI setup has to be optimized for every application to meet this criterion for reliable ICF diagnostics.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 3 03000e23 (2015)
The implementation and data analysis of an interferometer for intense short pulse laser experiments
Jaebum Park, Hector A. Baldis, and Hui Chen
We present an interferometry setup and the detailed fringe analysis method for intense short pulse (SP) laser experiments. The interferometry scheme was refined through multiple campaigns to investigate the effects of pre-plasmas on energetic electrons at the Jupiter Laser Facility at Lawrence Livermore National Laboratory. The interferometer used a frequency doubled (${\it\lambda}=0.527~{\rm\mu}\text{m}$) 0.5 ps long optical probe beam to measure the pre-plasma density, an invaluable parameter to better understand how varying pre-plasma conditions affect the characteristics of the energetic electrons. The hardware of the diagnostic, data analysis and example data are presented. The diagnostic setup and the analysis procedure can be employed for any other SP laser experiments and interferograms, respectively.
High Power Laser Science and Engineering
  • Publication Date: Aug. 03, 2016
  • Vol.4 Issue, 3 03000e26 (2016)
Using LiF crystals for high-performance neutron imaging with micron-scale resolution
A. Faenov, M. Matsubayashi, T. Pikuz, Y. Fukuda, M. Kando, R. Yasuda, H. Iikura, T. Nojima, T. Sakai, M. Shiozawa, R. Kodama, and Y. Kato
This paper describes an overview of our recent discovery – cleardemonstration that LiF crystals can be efficiently used as a high-performance neutronimaging detector based on optically stimulated luminescence of color centersgenerated by neutron irradiation. It is shown that the neutron images we haveobtained are almost free from granular noise, have a spatial resolution of and a linear response with a dynamic range of at least . The high contrast and good sensitivity of LiF crystals allow us todistinguish two holes with less than 2% transmittance difference. We propose to usesuch detectors in areas where high spatial resolution with high image gradationresolution is needed, including diagnostics of different plasma sources such as laserand z-pinch produced plasmas.
High Power Laser Science and Engineering
  • Publication Date: Jan. 01, 1900
  • Vol.3 Issue, 4 04000e27 (2015)
The application of proton spectrometers at the SG-III facility for ICF implosion areal density diagnostics
Xing Zhang, Jianhua Zheng, Ji Yan, Zhenghua Yang, Ming Su, Yudong Pu, Pin Yang, Xufei Xie, Li Chen, Ming Chen, Tianxuan Huang, Shao’en Jiang, Shenye Liu, and Jiamin Yang
Charged particle diagnostics is one of the required techniques for implosion areal density diagnostics at the SG-III facility. Several proton spectrometers are under development, and some preliminary areal density diagnostics have been carried out. The response of the key detector, CR39, to charged particles was investigated in detail. A new track profile simulation code based on a semi-empirical model was developed. The energy response of the CR39 detector was calibrated with the accelerator protons and alphas from a 241Am source. A proton spectrometer based on the filtered CR39 detector was developed, and D–D primary proton measurements were implemented. A step range filter spectrometer was developed, and preliminary areal density diagnostics was carried out. A wedged range filter spectrometer array made of Si with a higher resolution was designed and developed at the SG-III facility. A particle response simulation code by the Monte Carlo method and a spectra unfolding code were developed. The capability was evaluated in detail by simulations.
High Power Laser Science and Engineering
  • Publication Date: Oct. 29, 2015
  • Vol.3 Issue, 4 04000e28 (2015)